There are currently many radio/wireless and cellular access technologies and standards such as Global System for Mobile Communications/General Packet Radio Service (GSM/GPRS), Wideband Code Division Multiple Access/High Speed Packet Access (WCDMA/HSPA), CDMA-based technologies, wireless fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE), to name but a few. Numerous technologies and standards have been developed during the last few decades, and it can be expected that similar developments will continue into the future. Specifications are developed in a variety of organizations such as the 3rd Generation Partnership Project (3GPP), 3GPP2 and IEEE.
Communication between network nodes such as base stations and user equipment may be based on standardization, standard protocols and standard specifications, allowing the parties to the communication to interact appropriately. There are some scenarios, however, where a UE or network node operates in ways that are not defined by standard. Some UEs, for example, have performance limitations that prevent them from implementing all of the features required by a standard.
As an example, Category 0 UEs may have certain performance limitations because they may be equipped with only one receive antenna and/or because they may be limited to half-duplex operation. When such a UE enters an LTE network, an early task is to determine whether the network is capable of supporting such UEs. To support such UEs, the network is generally required to provide good coverage (e.g., via power boosting), since reception capabilities of these UEs may be relatively limited. Category 0 devices are defined in 3GPP Release 12, and they can optionally support HD Type B and can be produced with lower costs than other LTE UE categories. Release 13 defines category M UEs which will in most cases require HD operation.
In general, a duplex communication system is one that supports point-to-point communication between two parties in both directions. In a full-duplex (FD) communication system, the communication may occur in both directions at the same time, and in a half-duplex (HD) communication system, the communication may occur in only one direction at a time.
FD and HD operations are typically implemented using either time-division duplexing (TDD) or frequency division duplexing (FDD). In TDD, outward and return signals are communicated on the same carrier frequency, but at different times (e.g., in different time slots or non-overlapping subframes). In FDD, outward and return signals are communicated on different carrier frequencies, and can be communicated at the same or different times. In full-duplex FDD (FD-FDD) outward and return signals are communicated at the same time, and in half-duplex FDD (HD-FDD), outward and return signals are communicated at different times.
Certain communication standards such as Long-Term Evolution (LTE) provide for both TDD and FDD modes of communication, with the FDD mode being either an FD-FDD mode or an HD-FDD mode. The HD-FDD mode has the potential benefit, under certain frequency arrangements, of being implemented without a duplex filter. For instance, a device implementing HD-FDD may use a switch to change between different frequency channels rather than using a duplex filter to maintain concurrent communication on two different frequency channels. The omission of a duplex filter may allow such a device to be implemented at relatively lower cost and with lower power consumption compared to devices that require a duplex filter. Accordingly, the use of HD-FDD may be particularly attractive for certain low-cost applications. The HD-FDD mode also has the potential benefit of allowing FDD frequency bands that could not otherwise be used due to too narrow of a duplex distance.
Some envisioned uses of the HD-FDD mode include various forms of machine type communication (MTC), for instance in the so-called internet-of-things (IoT). MTC communication generally involves communication between machines and other machines (e.g., machine-to-machine communication) and/or between machines and humans. Such communication may include, for example, the exchange of measurement data, control signals, and configuration information. The machines involved in MTC may be of various forms and sizes, ranging from wallet-sized devices to base stations, for example. In many such applications, MTC devices are deployed in large numbers, with each device operating in infrequent bursts. Accordingly, it may be beneficial to reduce the cost and/or power consumption of each device by omitting a duplex circuit and relying on HD-FDD communication.
In certain contexts, such as LTE based systems, HD-FDD communication may occur between one or more devices that support HD-FDD but not FD-FDD communication (hereafter, an “HD-FDD device”), and one or more other devices that support both HD-FDD and FD-FDD communication (hereafter, an “FD-FDD device”). In such contexts, a scheduler in an FD-FDD device (e.g., an eNodeB) may be required to consider data and control traffic in both directions when making scheduling decisions for an HD-FDD device (e.g., a low-cost MTC device). This requirement tends to add complexity to the scheduler. For example, when not in discontinuous receive mode (DRX), the HD-FDD device may continuously receive information through downlink physical channels except e.g., when required to transmit HARQ feedback.
An HD FDD UE typically monitors transmissions on the physical dedicated control channel (PDCCH) and/or the dedicated physical control channel (DPCCH) when it is not required to transmit. Such downlink transmissions can be triggered by scheduling by the eNB or other UL transmissions that are not actively scheduled by the eNB such as transmission of scheduling request (SR), periodic channel state information (CSI) or preamble transmission on the physical random access channel (PRACH).
3GPP standardizes two types of HD FDD, including Type A HD FDD and Type B HD FDD. Type A HD FDD has a guard time created by the UE by not receiving the last part (approximately 20 μs) of the DL subframe immediately preceding an UL subframe from the same UE. Type B HD FDD has a HD guard subframe by not receiving a DL subframe immediately preceding or following an UL subframe. A UE may also be classified as Type A HD TDD or Type B HD TDD based on a similar configuration of guard time or guard frame, respectively.
An eNB cannot schedule the HD UE as a FD UE since it needs to keep track of UL subframes and guard subframes.
HARQ timing applies to HD UEs. For example, transmitting an UL grant to a UE in a subframe at n=0 (“n” denotes a subframe number) requires an UL subframe at n=4. If this is the only UL scheduling, then subframes at n=3 and n=5 will be guard subframes for a HD type B UE. As a consequence, the UE will not monitor the PDCCH at n=4, n=5 and n=6 and the eNB must secure that no DL transmissions are done at these subframes. Transmitting an UL grant to a UE at n=0 and a DL assignment at n=1 will create UL subframes where the UE will not monitor at n=3 to n=6, where n=3 and 6 are guard frames. Transmitting a DL assignment at n=0 and n=2 will create UL subframes at n=4 to n=6 (the UE needs to be in UL mode at n=5 to be able to transmit data in n=4 and N=6) and guard subframes at n=3 and n=7.
Future subframes change from DL to UL or guard depending on scheduling decisions, and the scheduler needs to be aware of guard and UL subframes to be able to schedule the UE. Keeping track of the link on a per millisecond basis is called dynamic scheduling. The scheduling decision shall take into account 3GPP defined HARQ timing in both UL and DL as explained above.